Target Cooling Through Gun Drilled Holes

ABSTRACT

A sputter target assembly particularly useful for a large panel plasma sputter reactor having a target assembly sealed both to the main processing chamber and a vacuum pumped chamber housing a moving magnetron. The target assembly to which target tiles are bonded includes an integral plate with parallel cooling holes drilled parallel to the principal faces. The ends of the holes may be sealed and vertically extending slots arranged in two staggered groups on each side and machined down to respective pairs of cooling holes on opposite sides of the backing plate in pairs. Four manifolds tubes are sealed to the four groups of slots and provide counter-flowing coolant paths.

RELATED APPLICATION

This application is a continuation of Ser. No. 11/190,389, filed Jul.27, 2005, incorporated herein by reference and now allowed.

FIELD OF THE INVENTION

The invention relates generally to sputtering apparatus. In particular,the invention relates to cooling of the sputtering target.

BACKGROUND ART

Sputtering is a well established technology in the fabrication ofsilicon integrated circuits, in which a metal target is sputtered todeposit target material onto the silicon wafer. Sputtering has also beenapplied to other uses, such as window coatings. In recent years,sputtering has also been applied for similar purposes as for siliconintegrated circuits in the fabrication of flat panel displays, such asflat computer displays and large flat televisions and the like. Varioustypes of flat panel displays may be fabricated typically including thinfilm transistors (TFTs) formed on large thin insulating rectangularsubstrates, often called panels, and including liquid crystal displays(LCDs), plasma displays, field emitters, and organic light emittingdiodes (OLEDs).

A conventional flat panel sputter reactor 10 is schematicallyillustrated in the cross-sectional view of FIG. 1. Demaray et al.(hereafter Demaray) disclose more details of such a reactor in U.S. Pat.No. 5,565,071, incorporated herein by reference. A pedestal 12 within amain vacuum chamber 14 supports a rectangular panel 16 to be sputtercoated in opposition to a generally rectangular target tile 18 bonded toa backing plate 20 sealed to but electrically isolated from the mainchamber 14 by an isolator 22. The panel 16 may be composed of a glass, apolymeric material, or other material. The target material is mosttypically a metal such as aluminum, molybdenum, or indium tin oxide(ITO) although other metals may be freely substituted depending on thetype of layer desired to be formed on the panel 16. Larger targets mayrequire the bonding of multiple target tiles to the backing plate inone- or two-dimensional arrays. An unillustrated vacuum pump systempumps the interior of the main chamber 14 to a base pressure of 10⁻⁶ to10⁻⁷ Torr or below. A gas source 24 supplies a sputter working gas suchas argon into the chamber 14 through a mass flow controller 26 and themain chamber pressure is kept typically at no more than a few milliTorrduring sputtering. A DC power supply 28 applies a negative DC bias ofseveral hundred volts to the target 18 in opposition to the groundedpedestal 12 and unillustrated chamber shield to cause the argon to beexcited into a plasma. The positively charged argon ions are attractedand accelerated by the negatively biased target 18 with sufficientenergy to sputter atoms of the target material from it. Some of thesputtered material strikes the panel 16 and coat it with a thin layer ofthe target material. Optionally, a reactive gas such as nitrogen, may beadditionally admitted to the chamber to cause the sputtered metal toreact with it and form a metal compound such as a metal nitride on thepanel surface.

Sputtering is greatly enhanced if a magnetron 30 having opposed magneticpoles is placed in back of the backing plate 20 to project a magneticfield B into the main chamber in front of the target 18. The magneticfield traps electrons and thus increases the density of the plasmaadjacent the target 18, greatly increasing the sputtering rate. Toachieve uniform erosion of the target 18 and uniform deposition on thepanel 16, the magnetron 30 is scanned in a one- or two-dimensionalpattern across the back of the backing plate 20. The form of themagnetron 30 may be much more complex than that illustrated.

Almost all panel fabrication equipment is distinguished by its largesize. The original generation was based on panels having lateraldimensions of the order of 500 mm. Various economic and product factorshave prompted successive generations of flat panel fabrication equipmentof ever increasing sizes. The next generation is being developed tosputter deposit on panels having sides of greater than 2 m. This largesize has introduced several problems not experienced in waferfabrication equipment limited to sizes of about 300 mm in the mostrecent equipment.

The target 18 and more particularly its backing plate 20 must berelatively thin so that the magnetron 30 can project a substantialmagnetic field through it. However, absent other means, the backingplate 20 needs to stand off a considerable force (differential pressuretimes the area) between its back and the high vacuum of the main chamber14 and further the backing plate 20 should not significantly bow underthese pressure differentials. To provide such large thin targets,Demaray proposed placing the magnetron 30 inside a magnetron chamber 32sealed to the back of the backing plate 20 and pumped to a relativelylow pressure in the sub-Torr range, the limit of a mechanical vacuumpump. Such back pumping reduces the force exerted on the backing plate20 by a factor of about a thousand.

Such a structure contrasts with a conventional wafer sputter reactor inwhich a corresponding chamber at the back of the target backing plate 20is filled with chilling water to cool the target during sputtering.Demaray, instead, recirculates cooling liquid from a chiller 34 throughcooling channels formed within the backing plate 32. As shown in thecross-sectional view of FIG. 2, a substantially rectangular conventionaltarget 40 includes a backing plate 42 formed of top and bottom plates44, 46. Cooling channels 48 of generally rectangular cross section aremachined into the surface of the top plate 44 to extend generallybetween the two sides of the backing plate 42 although larger horizontaldistribution manifolds may be formed nearer the two sides to connect thecooling channels 48 to a common cooling liquid inlet and a commoncooling liquid outlet. The bottom plate 46 is then bonded to the topplate 44 to enclose and seal the cooling channels 48 and manifolds. Atarget tile 50 is then bonded to the backing plate 42. In the past,indium bonding was most often used but conductive polymeric adhesivebonding is gaining favor.

The bonding of the two plates 46, 48 of the backing plate 42 haspresented technical challenges, particularly at the larger panel sizes.It is desired to reuse the backing plate 42 when sputtering haseffectively eroded through the target tile 50. That is, it is desired toremove the old target tile 50 and replace it with a new one. The backingplate 42 needs to be rugged to survive refurbishment when the usedtarget tile is delaminated from the backing plate and a new target tileis laminated. Targets and their backing plates have become increasinglyexpensive for the larger sizes of panels. Thus, their cost should bereduced while their ruggedness should be maintained and preferablyincreased. The two plates 44, 46 can be welded together, but weldingtends to deform thin plates. The two plates 44, 46 can be screwedtogether with a sealant placed in the interface. However, the number ofscrews required for a 2.5 m×2.5 m target becomes very large. Indiumbonding can be used, but its ruggedness is questionable. Autoclaving hasbeen suggested, but this is a complex and expensive process.

The larger target sizes have also presented a challenge in uniformlycooling a larger area without unduly increasing the thickness of thetarget assembly.

SUMMARY OF THE INVENTION

One aspect of the invention includes a sputtering target backing plateto which one or more target tiles are bonded and which has parallellaterally extending cooling holes formed parallel to the principalsurface of the backing plate for the flow of cooling water or otherliquid. The backing plate is preferably integral and cylindrical coolingholes may be bored across its lateral dimension, for example, by gundrilling.

Another aspect of the invention includes dividing the cooling holes intotwo interleaved groups and counter-flowing cooling liquid in the twogroups of cooling holes, that is, in anti-parallel directions to therebyreduce the temperature differential across the target and its backingplate.

A further aspect of the invention includes vertical inlet and outletholes or slots formed from a principal surface of the backing plate ontwo opposed peripheral sides and each joined to one or more of thecooling holes to supply and drain cooling liquid from the horizontallyextending cooling holes. The slots advantageously join two to sixadjacent cooling holes The ends of the cooling holes outside of thevertical and outlet holes are plugged. Advantageously, the holes orslots on each peripheral side alternate in offset along the axialdirection of the cooling holes to provide alternating inlet and outletholes or slots. Supply and drain manifolds may then be arranged inparallel and sealed to the respective inlet and outlet holes or slots.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a conventional flat panelsputtering chamber.

FIG. 2 is a cross-sectional view of a conventional target including abacking plate with cooling channels and a target tile bonded to it.

FIG. 3 is a schematic orthographic view of a simplified embodiment of abacking plate of the invention.

FIG. 4 is a cross-sectional view of a vertically extending cooling inletor inlet to a horizontally extending cooling hole.

FIG. 5 is a cross-sectional view of a plurality of horizontallyextending cooling holes formed in a target backing plate.

FIG. 6 is a bottom plan view of a multi-tile target and backing plate ofthe invention including four columns of cooling inlets and outlets.

FIG. 7 is an exploded orthographic view of a corner of the targetbacking plate of FIG. 6 including

FIG. 8 is an orthographic view of an embodiment of one of two coolingmanifolds to be attached to the backing plate of FIG. 6.

FIG. 9 is a plan view of a planar side of a manifold plate forming partof the manifold of FIG. 8.

FIG. 10 is an orthographic view of the backing plate of FIG. 6 to whichare attached two manifolds of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A backing plate 60 of one embodiment of the invention, veryschematically illustrated in the orthographic view of FIG. 3 from thebottom, is formed in an integral metal plate 62 having lateraldimensions corresponding to the desired size of the backing plate 60,for example, greater than 2 m on a side for the planned next generation.A series of parallel cylindrical cooling holes 64 are bored to extendfrom one lateral side to the other of the metal plate 62 and parallel tothe principal surfaces of the metal plate 62. Exemplary dimensions are athickness for an aluminum plate of 33 mm and hole diameter of 12 mm. Thehole boring over such a great distance may be achieved by gun drilling,that is, using a very long drill bit. In view of the long lengths, it isadvantageous to drill holes from both sides which join in the middle.The cooling water or other liquid flows through the holes 64 to cool thebacking plate 60 and hence the target tile affixed to the backing plate60.

In the illustrated embodiment, cooling water is supplied and drainedfrom elongated or oblong holes or slots 66, 68, 70, 72 milled from aprincipal surface of the metal plate 62 to preferably at least themedian depth of the holes 64 but not to the opposite side of the metalplate 62. As a result, the cooling holes 64 are exposed to respectivepairs of the slots 66, 68, 70, 72. The slots 66, 68, 70, 72 are locatedin two sets on opposed lateral sides of the metal plate 62 at positionsoutside of the vacuum chamber 14 and the magnetron chamber 32 to whichthe backing plate 60 will be sealed. For convenience of plumbingconnections, the slots are preferably located on the illustrated bottomside of the backing plate 60 to which the target tile will be bonded.Machining and sealing are simplified if the slots 66, 68, 70, 72 exposepairs of the cooling holes 64. The slots may be formed as circularholes, especially if they expose only one respective cooling hole butelongated slots linked to multiple cooling holes 64 are advantageous.More than two cooling holes 64 per slot would further simplify themachining and sealing but at the cost of degraded cooling uniformity.Generally, six cooling holes 64 per slot are a reasonable upper limit.As illustrated in the cross-sectional view of FIG. 4, the ends ofcooling holes 64 laterally outside of the slots 66, 68, 70, 72 are watersealed with plugs 74 so that the water flows from slot to slot onopposed sides of the backing plate 60 through the middle portion of thecooling holes 64.

The material of the backing plate 60 is not limited to aluminum oraluminum alloys but, in view of the gun drilling, it is preferred thatthe material be easily machinable, such as aluminum or brass.

It is preferred that the cooling water or other liquid coolant besupplied to and drained from the slots to set up counter flowingcoolant. For example, slot 66 can serve as in inlet and slot 68 as anoutlet for coolant flowing to the right and slot 72 can serve as aninlet and slot 70 as an outlet for coolant flowing to the left. Thecounter flow greatly reduces the temperature differential across thebacking plate 60 when there are many more anti-parallel flowing groupsof cooling holes 64. It is typical for cooling water to heat up fromabout 20° C. to 25° C. in one pass across the backing plate 60 undernormal sputtering conditions. For single directional flow, the backingplate 60 would have a similar 5° C. temperature differential from oneside to the other, which amounts to a differential thermal expansion ofabout 1 mm in aluminum, a value which should be reduced. On the otherhand, for counter flowing coolant neighboring pairs of cooling holes 64have an opposite temperature gradient and they are close enough that thebacking plate 60 is substantially cooled to the average of the twoflows, that is, a nearly constant 22.5° C. as averaged over the areabetween the counter-flowing holes although more localized butcompensating temperature variations will occur.

As illustrated in the cross-sectional view of FIG. 5, one or more targettiles 76 are bonded to the bottom side of the backing plate 60 (top asillustrated) in a target area 78 of FIG. 3 adjacent the cooling holes 64and between the slots 66, 68, 72, 72 providing coolant to them.

The illustration of the backing plate 60 of FIG. 3 is very simplified. Amore realistic target and backing plate assembly 80, illustrated in thebottom plan view of FIG. 6, includes an integral backing plate 82 withangled corners 84, which are illustrated in more detail in the explodedorthographic view of FIG. 7. It includes 42 parallel cooling holes 86 inalternating pairs for the counterflow. The cooling holes 86 may be aregun drilled from the opposed edges of the backing plate 82 including theangled corners 84. Exemplary dimensions are a thickness for an aluminumor aluminum alloy plate 82 of 33 mm and a hole diameter of 12 mm, thatis, a hole diameter of preferably greater than 25% and less than 75% andpreferably less than 50% of the plate thickness. The plate thickness maybe varied, for example, between 20 and 60 mm. Slots 88, 90 are machinedfrom the bottom operational surface of the backing plate 82 in twostaggered columns on each side to expose pairs of the cooling holes 88.Plural, for example, 10 sets of coupled slots 88 and plural, forexample, 11 sets of coupled slots 90 provide the pair-wise coupling ofthe slots 88, 90 to the cooling holes 86. As mentioned above, number ofcooling holes 88 exposed by a single slot 88, 90 may vary. Also, thenumber of slot sets may be varied but cooling uniformity is improved byincreasing the number of sets. Plugs 92 are screwed into or otherwisesealed to both ends of the holes 88, 90 so that all coolant flowsthrough the slots 88, 90. The plugs 92 may chosen from variouscommercially available types, for example, Swageloks, Farmington plugs,SAE plugs or they may be specially fabricated. A welded rod plug is alsopossible although warpage should be avoided.

The described embodiment evenly spaces the cooling holes 86 and slots88, 90 across the backing plate 82. However, non-uniform distributionsmay be used to tailor the cooling, for example, more cooling holes andhence more cooling in the center of the backing plate 82.

The described fabrication technique for an integral backing plate withcooling holes bored laterally therethrough provides several advantages.The fabrication based mostly on machining is much less expensive thanthe previously practiced bonding of multiple plates. Even if thediameter of the holes is a sizable fraction of the plate thickness, theydo not greatly reduce the plate's rigidity. Furthermore, the resultantbacking plate is not subjected to delamination during usage or targetrefurbishment.

After fabrication of the backing plate 82, target tiles 94 are bonded tothe backing plate 82, preferably with a conductive polymeric adhesive ina process available from TCB of San Jose, Calif. although conventionalindium bonding or other method may be used. The illustration showsmultiple tiles 94 in a two-dimensional array with predetermined gaps ofabout 0.5 mm between them, a useful arrangement if large target tilesare not readily available. However, other tile arrangements may be usedsuch as a one-dimension array of multiple tiles or a single large tile.

Two manifolds 100, one of which is illustrated in the orthographic viewof FIG. 8 generally from the bottom in their operational position, areattached to the opposed sides of the backing plate 82 on its operationalbottom side to cover and couple to the offset rows of slots 88, 90.Advantageously, they can easily formed of stainless steel withoutaffecting the cleanliness within the sputtering chamber. Each manifold100 includes a manifold plate 102 and a short rectangular manifold tube104 and a long rectangular manifold tube 106, each having respectivepairs of hose fittings 108, 110 for the supply and draining of coolingwater or other liquid coolant through unillustrated hoses to the chiller34. Multiple holes fittings 108, 110 mounted on and coupled to theinteriors of each manifold tube 104, 106 provide a more uniform flow ofcoolant to each of the large number of slots 88, 90 and associatedcooling holes 86. The two manifold tubes 104, 106 are welded from withineach of the manifold plate slots 112, 114 between the slot periphery andthe manifold plate 106. When welded, the two manifold tubes 104, 106 areseparated by about 1 cm between them to allow screwing of fastenersbetween the manifold plate 106 and the backing plate 82 in the areabetween the manifold tubes 104, 106.

The manifold plate 102, as shown in the top plan view of FIG. 9 includestwo staggered rows of manifold slots 112, 114 in correspondence to theslots 88, 90 in the backing plate 82. O-ring grooves 116 surround eachof the manifold slots 112, 114 to accept respective O-rings used to sealthe manifold 100 and its slots 112, 114 to the backing plate 82 aroundits slots 88, 90. The bases of the manifold tubes 104, 106 havecorresponding slots machined into them to allow cooling liquid to freelycirculate between the manifold tubes 104, 106 and the correspondinggroups of the cooling holes 86. Three rows of unillustrated throughholes bored through the manifold plate 102 match correspondingunillustrated tapped holes in the backing plate 82 for screw attachmentand sealing of the manifold 100 to the backing plate 82. The through andtapped holes are arranged such that four screws are fastened in arectangular pattern around each of the manifold slots 112, 114 touniformly seal the O-rings 116.

An operational target assembly 120 is illustrated in the partialorthographic view of FIG. 10 generally from the bottom in it operationalorientation. The operational target assembly 120 includes the target andbacking plate assembly 80 of FIG. 8 and two manifolds 100 of FIG. 8(only one of which is illustrated) fixed and sealed to two opposedperipheral sides of the backing plate 82 outside of its vacuum seals tothe main and magnetron chambers 14, 32. The operational target assembly120 additionally includes a multi-branch supply hose 122 and amulti-branch drain hose 124 connected between a chiller 118 and the hosefittings 108, 110 on both lateral sides of the backing plate 82. On theillustrated manifold 100, the supply hose 122 supplies chilled coolantto the short manifold tube 106 while the drain hose 124 drains coolantwarmed by the target from the long manifold tube 106. The double hoseconnection to each manifold tube 104, 106 evens the flow between thelarge number cooling holes. In contrast, on the unillustrated manifold100 fixed to the other unillustrated lateral side of the target 80 withsimilar hose fittings 108, 110, the supply hose 122 supplies chilledcoolant to the long tube manifold tube 106 through the two hose fittings110 and the drain hose 124 drains warmed coolant from the short manifoldtube 104 through the two hose fittings 108. As a result, a first coolantflow is set up in one direction between the two short manifold tubes 104and a second coolant flow is set up in the opposite direction betweenthe two long manifold tubes 106.

The external manifolds provide several advantages of their own. They canbe manufactured separately from the target assembly and can be easilyreused. Furthermore, in combination with the large number of parallelcooling holes, they enable a more uniform cooling of the target.

An alternative embodiment includes a single row of backing plate slots88, 90 on both principal surfaces of the backing plate 82 and on bothits lateral sides connecting to different ones of the cooling holes 64.Separate liquid manifolds may be affixed to the top and bottom of thebacking plate 82. This configuration reduces the length of the backingplate. Yet other forms of the manifolds are included within theinvention.

Although the above embodiments have been described with respect to theorientations of the sputter chamber of FIG. 1, it is clear that theorientation may be inverted, put on its side, or arranged at anotherangle without departing the spirit of the invention. The directionsrecited in the claims are for convenience only and may be changed toother orientations with respect to gravitational force.

The invention is not limited to sputtering onto panels intended fordisplays but may be applied to other applications.

The several features of the invention may be practiced separately or incombination and with limitations restricted only by the claims.

The invention thus provides a less expensive, more rugged targetassembly and reusable backing plate providing improved thermal control.

1. A sputtering target, comprising: a backing plate formed in a metalplate having two parallel principal surfaces and including a pluralityof cooling channels formed in parallel cooling holes which extendlaterally parallel to a common axis from a first lateral side to anopposed second lateral side of the metal plate and which are formed inthe metal plate with inner portions that are cylindrically shaped; andone or more sputtering target tiles bonded to one of the two principalsurfaces in a target area of the backing plate underlain by the innerportions of the cooling holes.
 2. The target of claim 1, wherein thebacking plate is an integral plate formed without bonding of multiplemembers to form the backing plate, wherein the principal surfaces areplanar.
 3. The target of claim 1, wherein the cooling holes are adaptedto be coupled to at least one liquid cooling supply line and to at leastone liquid cooling drain line.
 4. The target of claim 1, furthercomprising a plurality of inlet holes and a plurality of outlet holesextending from at least one of the principal surfaces to the coolingholes.
 5. A sputtering target, comprising: a backing plate formed in ametal plate having two parallel principal surfaces including oneprincipal surface adapted to be bonded to one or more sputtering targettiles, the backing plate including a plurality of parallel coolingchannels formed in cooling holes formed in the metal plate having atleast portions that are cylindrically shaped and underlie the targetarea and which extend laterally parallel to a common axis from a firstlateral side of the metal plate to a second lateral side of the metalplate opposed to the first lateral side; and sealing members extendingalong respective axes parallel to the common axis and fit in and sealingand plugging the cooling holes at the opposed lateral sides.
 6. Thetarget of claim 5, wherein the backing plate has a substantiallyrectangular shape.
 7. The target of claim 5, wherein the one or moretarget tiles are bondable to the backing plate in a substantiallyrectangular area.
 8. The target of claim 5, wherein the sealing membersare plugs screwed into ends of the cooling holes at the lateral edges ofthe metal plate.
 9. The target of claim 5, wherein the backing platefurther includes in an area of the backing plate outside of the targetarea inlet and outlet holes extending from at least one of the principalsurfaces to the cooling holes.
 10. The target of claim 9, wherein someof the inlet and outlet holes are coupled to a respective plurality ofthe cooling holes in first alternating groups thereof on opposed lateralsides of the backing plate and others of the inlet and outlet holes arecoupled to another respective plurality of the cooling holes in secondalternating groups thereof on the opposed lateral sides of the backingplate.
 11. The target of claim 10, wherein the pluralities are between 2and
 6. 12. The target of claim 10, further comprising four liquidmanifolds coupled to respective ones of two of the groups on two opposedlateral sides of the backing plate.
 13. The target of claim 12, furthercomprising two manifold plates to which are fixed respective pairs ofthe liquid manifolds and which are detachably affixable to the backingplate.
 14. The target of claim 13, further comprising O-rings sealingthe manifold plates to the backing plate.
 15. The target of claim 9,wherein the inlet and outlet holes include elongate slots formed withelongate cross section in the backing plate and each communicating witha plurality of the cooling holes.
 16. The target of claim 9, wherein aplanar portion of the metal plate between the inlet and outlet holes andthe target area allows vacuum sealing to a vacuum chamber.
 17. Asputtering chamber, comprising: the target of claim 9; a main vacuumchamber sealed to the backing plate with the sputtering target tilesfacing the processing chamber and including a pedestal facing the one ormore sputtering target tiles for supporting a substrate to be sputtercoated from the one or more sputtering target tiles; and a vacuum pumpedmagnetron chamber sealed to the backing plate on a side thereof oppositethe one or more sputtering target tiles for accommodating a magnetronscanned adjacent the backing plate; wherein the outlet holes of thebacking plate are disposed outside of vacuum seals sealing the backingplate to the main vacuum chamber and to the magnetron chamber.
 18. Asputtering target backing plate formed by the process comprising:drilling a plurality of cylindrical first holes in a metal plate betweena first lateral side of the metal plate and a second lateral side of themetal plate opposed to the first lateral side so as to extend parallelto a principal surface of the metal plate, a plurality of coolingchannels being formed in inner portions of the first holes away from thefirst and second lateral sides; milling second holes to extend betweenthe principal surface and the inner portions of the respective firstholes disposed between the plugs and arranged on each side of a centralarea of the metal plate overlying cylindrical portions of the firstholes and adapted to be bonded to one or more sputter tiles; andinserting plugs into, filling, and fluid sealing ends of the first holesadjacent the first and second lateral sides.
 19. The backing plate ofclaim 18, wherein each of the second holes extends to a plurality of thefirst holes.
 20. The backing plate of claim 18, wherein the processfurther comprises bonding one of more target tiles to the central areaof the metal plate.